The present invention relates generally to a device and method for dressing or conditioning a CMP pad. More particularly, the present invention relates to a dressing disk of a super hard material, such as diamond or cubic boron nitride, for dressing or conditioning a CMP pad. Even more particularly, the present invention relates to a dressing disk having evenly spaced abrasive particles thereon, which is coated with a thin film of diamond like carbon for protection from chemical attack.
Many industries are now using a chemical mechanical process (CMP) for polishing certain work pieces. Particularly, the computer manufacturing industry has begun to rely heavily on CMP processes for polishing wafers of ceramics, silicon, glass, quartz, and metals thereof. Such a polishing process generally entails applying the wafer against a rotating pad made from a durable organic substance such as polyurethane. To the pad, is added a chemical slurry containing a chemical capable of breaking down the wafer substance, and an amount of abrasive particles which act to physically erode the wafer surface. The slurry is continually added to the spinning CMP pad, and the dual chemical and mechanical forces exerted on the wafer cause it to be polished in a desirable manner.
Of particular importance to the quality of polishing produced, is the distribution of the abrasive particles throughout the pad. The top of the pad holds the particles, usually by a means such as fibers, which provide the friction necessary to allow the abrasives to act on the wafer, rather than being thrown off of the pad. Therefore, it is extremely important to keep the top of the pad as flexible as possible.
A problem with maintaining the top of the pad is due to the accumulation of polishing debris coming from the work piece, abrasive slurry, and dressing disk. This accumulation causes a xe2x80x9cglazingxe2x80x9d or hardening of the top of the pad, which makes the pad less able to hold the abrasive particles of the slurry.
Therefore, attempts have been made to revive the top of the pad by xe2x80x9ccombingxe2x80x9d it with various devices. This process has come to be known as xe2x80x9cdressingxe2x80x9d or xe2x80x9cconditioningxe2x80x9d the CMP pad. Many types of devices and processes have been used for this purpose. One such device is a disk with a plurality of super hard crystalline particles, such as diamond particles attached to a surface, or substrate thereof.
Unfortunately, such diamond disks made by conventional methods exhibit several problems. First, diamonds have become dislodged from the substrate of the disk and are caught in the CMP pad fibers. This leads to scratching of the work piece being polished. Second, the production methods of the past tend to produce disks having diamonds that are clustered in groups, or unevenly spaced on the surface of the substrate. This uneven grouping causes some portions of the CMP pad to be overdressed which creates wear marks, while others are underdressed which creates glazing layers. In either case, pad polishing efficiency is reduced, and uneven polishing occurs. Finally, the diamonds of these disks do not extend to a uniform height above the substrate surface of the disk. This non-uniformity additionally creates uneven dressing of the CMP pad, because many particles from the dresser may not touch the pad.
The dislodging of diamonds from the disk substrate is due to the inferior method by which they have been attached. When diamonds are held by electroplated nickel to the substrate, there is no bonding force but mechanical locking of the diamond. Hence, these particles will become dislodged as soon as they are rocked loose. This dislodgement process is facilitated by the chemical attack on the electroplating material which is presented by the chemical slurry.
On the other hand, when diamonds are brazed onto the substrate, the chemical force holds the diamond more firmly. However, the acids of the chemical slurry quickly weaken the braze-diamond bonds and dislodge the diamonds under the friction of pad dressing. Therefore, to minimize the exposure of the braze to the chemicals, the polishing processes was halted while the dressing occurred, and then started again. This sequence of alternately polishing and then dressing wastes an enormous amount of time, and is extremely inefficient.
In view of the foregoing, a CMP pad dresser which provides an even grooming of the CMP pad is desirable. Additionally, a CMP pad dresser which grooms a CMP pad to an even depth is very desirable. Further, a CMP pad dresser which is less susceptible to diamond particle dislodgment is highly desirable. Finally, a CMP pad dresser which may resist the acid attack of a chemical slurry, and continually dress the CMP pad, even while polishing is being performed, is extremely desirable.
It is therefore an object of the present invention to provide a CMP pad dresser which is capable of using abrasive particles to evenly dress or condition, the CMP pad.
It is an additional object of the present invention to provide a CMP pad dresser which is less susceptible to abrasive particle dislodgement.
It is another object of the present invention to provide a CMP pad dresser which is corrosion resistant so that it is capable of constantly dressing a CMP pad, even while the pad is engaged in the act of polishing.
It is also an object of the invention to provide a chemical barrier that prevents the dissolution of elements from the disk which will contaminate a wafer being polished.
It is a further object of the invention to provide a method of dressing or conditioning a CMP pad evenly.
It is additionally an object of the present invention to provide a method of reducing the susceptibility of a CMP pad dresser to abrasive particle dislodgment even when the pad is immersed in an acid slurry.
The above objects and others not specifically recited are achieved in a specific illustrative embodiment of a CMP pad dresser which has a plurality of evenly spaced abrasive particles affixed to a substrate. Generally, the particles are of a super hard substance such as diamond, or cubic boron nitride (cBN), in either the single crystal or polycrystalline form.
In one method of forming the CMP pad dresser of the present invention, a braze powder and an organic binder are first mixed thoroughly to form a dough. The dough is then rolled between two rollers to form a flexible sheet of brazing alloy. The abrasive particles are then evenly placed on the sheet of brazing alloy by use of a template which contains a plurality of evenly spaced apertures. The apertures of the template are larger than the size of one abrasive particle or xe2x80x9cgrit,xe2x80x9d but smaller than the size of two. Once all the apertures have been filled with abrasive particles, any excess abrasive particles are removed, and the abrasive particles are pressed into the brazing alloy sheet to embed them therein, by using a generally flat surface such as a steel plate. The template is then removed, and the abrasive particle containing brazing alloy, is affixed to the substrate with an acrylic glue. Finally, the whole assembly is brazed in a vacuum furnace to complete the brazing process and firmly fix the abrasive particles to the substrate.
Alternatively, the abrasive particles may be affixed to the substrate with an acrylic glue, using the template as described above. Next, the brazing alloy particles are showered onto the abrasive particles and substrate. Finally, the whole assembly is heated in a vacuum brazing furnace to complete the brazing process and firmly affix the abrasive particles to the substrate.
By using the template to place the abrasive particles in a controlled manner, any desired pattern of placement may be achieved. This pattern may be nearly any conceivable pattern, but most importantly provides the ability to evenly space the abrasive particles on the substrate. Additionally, by using a template with uniformly sized apertures, a uniform size of each abrasive particle is ensured. Finally, using a flat surface to press the abrasive particles into the substrate, creates a uniform height of the abrasive particles protruding above the substrate surface. This uniform height of abrasive particles ensures plowing, or dressing of the CMP pad to a uniform depth. Further, the uniform distribution of the abrasive particles across the substrate allows for a uniform dressing of the pad across its surface.
After affixing the abrasive particles to the substrate, a thin coating of additional anti-corrosive material may be applied to the CMP pad dresser. Such a coating effectively xe2x80x9csealsxe2x80x9d the surface of the CMP pad dresser. Such a sealant protects the abrasive particles and the braze, or other fixing agent and reduces their susceptibility to chemical attack from the chemicals of the abrasive slurry, especially those slurries containing acids. As the face of the CMP pad dresser is rendered less susceptible to chemical degradation, so also is lessened its susceptibility to abrasive particle dislodgement. Therefore, the CMP pad dresser is able to continually dress the CMP pad, even during a polishing act, because the agent binding the abrasive particles to the substrate is protected from chemical degradation.
The above and other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings.